Wireless communication systems commonly include information carrying modulated carrier signals that are wirelessly transmitted from a transmission source to one or more receivers within an area or region.
Wireless communication systems serving stationary and mobile wireless subscribers are rapidly gaining popularity, resulting in a need for greater efficiency in the use of the available radio frequency spectrum. This goal has been complicated because wireless communications channels between transmit and receive devices are inherently variable, so the characteristics of wireless channels, such as signal quality, generally vary in time, frequency and space. Under good conditions wireless channels exhibit good communication parameters, e.g., large data capacity, high signal quality, high spectral efficiency and throughput. However, under poor channel conditions, these parameters have significantly lower values. For example, when the wireless channel is degraded the transmitted data may experience excessive corruption, manifesting as high bit-error rates or packet error rates. The degradation of the channel can be due to a multitude of factors such as general noise in the channel, multipath fading, loss of line-of-sight path, excessive Co-Channel Interference (CCI) and other factors.
Motivated by these complications, prior art wireless systems have employed adaptive modulation of the transmitted signals with the use of feedback from the receiver as well as adaptive coding and receiver feedback to adjust data transmission to changing channel conditions. Such adaptive modulation has been applied to Single Input Single Output (SISO) as well as to Multiple Input Multiple Output (MIMO) systems, e.g., systems with antenna arrays at both the transmit and receive ends.
In some wireless system, some receivers suffer from poor channel conditions that cannot be acceptably improved through adaptive modulation or adaptive coding. The receivers are generally receivers that are physically located a large distance from the transmitter, or are located such that transmission signal to the receiver suffer a great amount of signal loss.
It is desirable to have a system and method that provides adaptive transmission to receivers suffering from excessive signal loss.